Effect of molecular interactions between saccharides residues on stability of colloidal particles

BENÍTEZ ELISA INÉS; PETELSKI, NICOLAI; LOZANO JORGE ENRIQUE; PERUCHENA NÉLIDA MARÍA; SOSA, GLADIS LAURA

Santiago

Congreso; 10th Congress of the World Association of Theoretical and Computational Chemists (WATOC 2014); 2014

Pontificia Universidad Católica de Chile

From a physicochemical point of view a cloudy apple juice is a colloidal suspension. The continuous medium is a solution of pectin, sugars and malic acid, and the dispersed matter is mainly formed by cellular tissue comminuted during fruit processing. The particles are mainly composed of carbohydrates and proteins. During the production of clarified juices the native pectin must be enzymatically degraded since it complicates the clarification process. After juice depectinization, the negative part of a colloid which is not degraded; interact with the degraded part of other colloid. These interactions are attractive and generate agglomeration and finally the flocculation of particles. Nevertheless, after this treatment, still remain cellular tissue, that continue causes appreciable turbidity to the juice. A previous study has shown that particles are inherently stable and possess a high affinity for water. One possible explanation is that they are strongly hydrated by an immobilized water layer coating them. In order to understand the mechanism by which the particles remain in suspension, in this work we have simulated a small fragment of colloidal particle by Molecular Dynamic and studied their interaction with the solvent (Figure 1). In order to study the interactions intra-fragment in water, a representative fragment of type II arabinogalactan was selected. This fragment consists of 4 -D-galactopiranosyl unit (backbone) and a disaccharide formed by -D-galactopiranosyl unit and -L-arabinofuranosyl unit (side-chain). Previously, conformational analysis was performed. The system consists of a type II arabinogalactansolvated in NNN molecules of water. The fragment of carbohydrate was constructed with the Glycam carbohydrate builder. MD simulations were performed with Amber 11, and the interactions intra-fragments were analyzed by the Quantum Theory of Atoms In Molecules (QTAIM) of Bader. The wave function was obtained at the B3LYP/631G* level of theory. This study has revealed the importance of the hydrogen bonds which occur between the side-chain and main-chain atoms and how these bonds vary in presence of water molecules that form the hydration layer of the fragment. These results also demonstrate that the polysaccharide which surrounds the particles is strongly hydrated, verifying the previously proposed hypothesis.